This book constitutes the refereed proceedings of the 19th International Conference on Software Engineering and Formal Methods, SEFM 2021, held as a virtual event, in December 2021. The 22 full papers presented together with 4 short papers were carefully reviewed and selected from 86 submissions. Also included are 2 invited talks and an abstract of a keynote talk. The papers cover a large variety of topics, including testing, formal verification, program analysis, runtime verification, meta-programming and software development and evolution. Chapter 'Configuration Space Exploration for Digital Printing Systems' is available open access under a Creative Commons Attribution 4.0 International License via link.springer.com.